In the past, efforts were concentrated on getting the nozzle flow stream to reach as far out as possible for the pressure available. For the close-in coverage, smaller secondary nozzles or slots were provided with sharp corner passages as well as the use of a break-up screw which could be adjusted into the main stream to provide the near field spray pattern desired. This approach, however, caused significant reduction in range and its adjustment was subjective on the part of the person doing the adjustment.
Sharp cornered, small passages provide reduced range precipitation but have relied primarily on fogging at the edges to provide coverage closer than six to twelve feet at pressures of greater than 30-40 PSI.
With the advent of computer, finite element analysis of the precipitation fall out from data provided from catch cups placed on the ground in a sprinkler's pattern, it has become obvious of the importance of being able to achieve a particular precipitation pattern relative to a particular placement of other sprinklers and the effects of interacting patterns between sprinklers. Computer modeling shows the importance of being able to provide uniform close-in precipitation from a sprinkler without producing driving sprays against the ground or fogging which is more easily blown away by the wind from the intended fallout area.
Computer modeling of some sprinkler spacing patterns require the precipitation rate (inches/hour/square foot) to be a maximum at the sprinkler and to decrease uniformly out to its maximum range of coverage which is still desired to be as great (far out) as possible for the water pressure that is available. Often pressure of greater than 30 PSI is required for some of the existing nozzles to provide sufficient stream turbulence for even marginal close in coverage and there are many complaints of dry donut-shaped areas close in around the sprinklers.
Additional parts or nozzles and required adjustments or assembly increase the cost of manufacture of the sprinkler and if it relies on someone to make adjustments, it does not provide the inherent uniformity of a single piece nozzle that has multiple features to provide the desired precipitation pattern.
In my U.S. Pat. No. 4,867,378, issued Sept. 19, 1989 and divisional patent application Ser. No. 403,758, filed Sept. 6, 1989, I disclose a single piece nozzle with a staggered secondary nozzle passage for providing close-in coverage with great ease and precision of manufacture. In my patent application Ser. No. 516,362, filed Apr. 30, 1990, I disclose and claim a sprinkler having a nozzle with secondary flows which impinge on each other.